The effect of Phencyclidine on neural activity in vestibular and supplementary motor cortex of primates will be studied for the purpose of further elaborating a conception developed in earlier work in this laboratory: namely, that phencyclidine affects preferentially the phylogenetically more primitive sensory-motor projection systems which regulate integrated movements of body core and proximal limbs, as a prerequisite for exercising the discriminative and discrete function of distal (apical) body parts, subserved by the phylogenetically more recent pre- and postcentral koniocortex. The comparative study with other hallucinogenic agents is expected to test the validity of the working hypothesis that the disruption of the normal function of the more primitive neural system is a common feature in drug induced perceptual aberrations.